linux-kernel - Re: [PATCH V4 11/22] LoongArch: Add process management

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Message-ID: <CAAhV-H5ndJvpcZ3P0P-65_-MFmpLuZ7k8Be6vUAFaL--sXDtxg@mail.gmail.com>
Date:   Sun, 3 Oct 2021 17:10:58 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V4 11/22] LoongArch: Add process management

Hi, Al,

On Sun, Oct 3, 2021 at 10:50 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Mon, Sep 27, 2021 at 02:42:48PM +0800, Huacai Chen wrote:
>
> > +/*
> > + * Does the process account for user or for system time?
> > + */
> > +#define user_mode(regs) (((regs)->csr_prmd & PLV_MASK) == PLV_USER)
> > +
> > +static inline int is_syscall_success(struct pt_regs *regs)
> > +{
> > +     return !regs->regs[7];
> > +}
> >
> > +static inline long regs_return_value(struct pt_regs *regs)
> > +{
> > +     if (is_syscall_success(regs) || !user_mode(regs))
> > +             return regs->regs[4];
> > +     else
> > +             return -regs->regs[4];
> > +}
>
> Huh???  That looks like you've copied those from MIPS, but on MIPS we have
> things like
>         li      t0, -EMAXERRNO - 1      # error?
>         sltu    t0, t0, v0
>         sd      t0, PT_R7(sp)           # set error flag
>         beqz    t0, 1f
>
>         ld      t1, PT_R2(sp)           # syscall number
>         dnegu   v0                      # error
>         sd      t1, PT_R0(sp)           # save it for syscall restarting
> 1:      sd      v0, PT_R2(sp)           # result
> right after the call of sys_...(), along with the restart logics
> looking like
>         if (regs->regs[0]) {
>                 switch(regs->regs[2]) {
>                 case ERESTART_RESTARTBLOCK:
>                 case ERESTARTNOHAND:
> IOW, syscall return values from -EMAXERRNO to -1 are negated, with
> regs[7] set accordingly.  Nothing of that sort is done in your
> patchset after syscall, and if it had been, your restart logics in
> signal handling would've been wrong anyway.
>
> What's going on there?
Sorry, the code derived from MIPS is wrong here, regs_return_value
should simply return regs->regs[4].

Huacai